In a Cognitive Radio (CR) system, a wireless communication device having a cognitive function can use a licensed frequency band in a kind of ‘opportunistic’ manner on the premise of causing no interference to a licensed user, which greatly increases the utilization rate of spectrum and resolves the conflict between the increasing demand for wireless services and continuously scarcity of frequency resources. CR technologies allocate spectrum among systems dynamically, breaking through the conventional fixed spectrum allocation and increasing the utilization rate of spectrum. As one of core technologies of CR, dynamic spectrum allocation technology has become a research hotspot.
In CR, the sensing on a radio environment improves the management on radio resources and facilitates the monitoring on a network and the handling of a failure. Radio Environment Maps (REM) refer to a dynamic database which is capable of tracking the change of a radio environment and in which wireless related measurements of positioning information and network performance indicators are stored. Wireless related measurements include Reference Signal Receiving Power (RSRP)/Reference Signal Receiving Quality (RSRQ) measurement, interference level measurement and Quality of Service (QoS) measurement. REM assists in a CR decision.
Researches show that the current utilization rate of TV spectrum is not high, thus, CR can wait an opportunity to use a channel which is not used by a primary system (that is, a television broadcasting system) at a specific time at a specific position, that is, a Television White Space (TVWS); to protect the primary system from being interrupted by a secondary system (that is, a CR system), the distance between the transmitter of the secondary system using an idle spectrum of the primary system and the coverage edge of the primary system is greater than a certain value, and this value is the protection distance between the primary system and the secondary system. FIG. 1 is a diagram illustrating a system architecture for the use of a TVWS by a CR system according to the prior art, as shown in FIG. 1, the main network elements involved include: a Database (DB), a Central Control Point (CCP) and a Base Station (BS), wherein the DB contains information on the spectrum occupied by a primary user, information on the spectrums not occupied by the primary user and information on spectrums not allowed to be used; the CCP manages the access of a subordinate node to the TVWS and coordinates the allocation of the TVWS spectrum to the subordinate nodes; the CCP is fixedly connected with the DB to acquire TVWS spectrum information and synchronously fixedly or wirelessly connected with the BS; the BS having a reconfiguration function and a cognitive function is capable of changing or adjusting parameters (e.g. modulation type and transmitting power) of wireless communication technologies, managing and maintaining an operating spectrum (e.g. an operating frequency point and a bandwidth) and has a spectrum cognition capability and a cognitive data processing capability.
Typically, according to the prior art, in the dynamic spectrum allocation technology, a base station needing to apply for a spectrum resource applies for a spectrum resource from a CCP, the CCP requests a DB for the allocation of a spectrum and then coordinates the allocation of spectrum resources according to the requested spectrum resource and the spectrum use condition of subordinate nodes. During the dynamic spectrum allocation process, since every time the base station needing to apply for a spectrum resource sends a spectrum resource application, the CCP needs to access the DB and coordinate the allocation of a spectrum to the BS applying from a spectrum resource according to the spectrum use condition of subordinate nodes, it takes a certain time to complete the processing process, causing a delay in the allocation of the spectrum resources and consequentially leading to a delay in the reconfiguration of spectrum resources.
A channel management method is proposed in the IEEE802.22 Wireless Regional Area Networks (RWAN) protocol according to which available channel list (that is, a set of channels potentially available to a secondary system provided by a DB according to the position of the secondary system) are divided into six types of channel sets: a set of channels not allowed to be used, a set of operating channels, a set of backup channels, a set of candidate channels, a set of protected channels and an unclassified channels. The channel not allowed to be used refers to a channel not allowed to be used by the secondary system for the sake of a service requirement or the restriction of a local rule; the operating channel refers to the current channel used for the communication of a BS in a WRAN cell with Customer Premise Equipments (CPEs); the backup channel refers to a channel which can function as an operating channel at any time if needed; the candidate channel refers to a channel which can function as a backup channel (the possibility that a candidate channel can function as a backup channel is evaluated by sensing the candidate channel); the protected channel refers to a channel which is being used by a primary user or a WRAN user according to a sensing result; and the unclassified channel refers to a channel that has not been sensed which can be determined as a candidate channel or protected channel according to a sensing result. Different channel sets have different sensing periods, by defining channel sets, a channel can be selected from a set of backup channels when a secondary system needs a spectrum so that the secondary system can use an idle spectrum not used by a primary system on the premise of causing no interference to the primary system. The channel classification method takes into consideration of the occupation status of channels, regulatory constraints and the quality status of channels, however, secondary systems different in configuration and providing different services have different requirements on spectrum, for example, if secondary systems have different requirements on transmitting parameter and the quality of service (QoS), they will have different requirements on spectrum, in addition, the natural isolators existing in the radio environment of a secondary system, for example, the high buildings or mountains located on the coverage edge of the base station of a secondary system, also cause influence on the spectrum selection of the secondary system. The channel set management taking no consideration of these factors degrades the quality of service after reconfiguration and even leads to a failed reconfiguration.
To address the foregoing problems existed in the prior art, a dynamic spectrum allocation method is proposed in the present disclosure.